1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD panel that prevents luminance occurring in a contour of a cell region from being higher than that occurring in the cell region, thereby improving picture quality.
2. Discussion of the Related Art
Rapid development within the fields of information and communication has caused an increase in the demand for thin, lightweight and low cost display devices for viewing information. Industries that develop displays are responding to these needs by placing high emphasis on developing flat panel type displays.
Historically, the Cathode Ray Tube (CRT) has been widely used as a display device in applications such as televisions, computer monitors, and the like, because CRT screens can display various colors with high luminance. However, the CRT cannot adequately satisfy present demands for display applications that require reduced volume and weight, portability, and low power consumption, while having a large screen size and high resolution. Out of this need, the display industry has placed high emphasis on developing flat panel displays to replace the CRT. Over the years, flat panel displays have found wide use in monitors for computers, spacecraft, and aircraft. Examples of flat panel display types currently used include the LCD, the electroluminescent display (ELD), the field emission display (FED), and the plasma display panel (PDP).
Characteristics required for an ideal flat panel display include a lightweight, high luminance, high efficiency, high resolution, high speed response time, low driving voltage, low power consumption, low cost, and natural color.
Generally, a phosphor material on a surface of the CRT emits light in an analog type based on an externally applied display timing signal and an externally applied data signal, so that a trace of an electron beam is controlled. On the other hand, the LCD controls the electric field applied to the liquid crystal located in each display so that transmittivity of light is controlled.
Development and application of thin film transistor (TFT)-LCD industries have been accelerated in accordance with the increase in the dimensions and increase in the resolution. To increase the productivity, many efforts have been focused on simplifying process steps and improving yield.
A related art LCD panel is now described with reference to FIG. 1.
FIG. 1 is a plan view illustrating a related art LCD panel.
As shown in FIG. 1, a plurality of gate lines G1, G2, . . . , Gn are arranged to cross a plurality of data lines D1, D2, . . . , Dn, so that a plurality of pixel regions are defined. A TFT is formed at each crossing point between the respective gate line and the respective data line. A pixel electrode 15 is formed in each pixel region.
The TFT includes a gate electrode 11 extending from the gate lines, a gate insulating film (not shown) over the gate electrode, a semiconductor layer 12 on the gate insulating film, and source and drain electrodes 13 and 14 on the semiconductor layer 12.
All the gate lines G1, . . . , Gn have substantially the same widths as one another. All the data lines D1, . . . , Dn also have substantially the same widths as one another.
A pixel electrode 15 including a transparent conductive material such as indium tin oxide (ITO) is formed in each pixel region. Each pixel electrode 15 has the same aperture ratio over the entire region of the panel.
As shown in FIG. 1, no pixel electrode is formed above the first gate line G1. Likewise, no pixel electrode is formed before the first data line D1 and the nth data line Dn.
The process for fabricating the aforementioned related art LCD panel will now be described with reference to FIG. 2A to FIG. 2C.
As shown in FIG. 2A, a gate electrode material, such as Al, Cr, Mo, Ta, and Al alloy, is formed on an insulating substrate by a sputtering process and then is patterned, so that the plurality of gate lines G1, G2, . . . , Gn having the gate electrode 11 are formed to have substantially the same widths.
Afterwards, the gate insulating film (not shown) of SiNX or SiOX is formed on the entire surface including the gate lines G1, G2, . . . , Gn. As shown in FIG. 2B, a semiconductor layer 12 used as a channel of the TFT is patterned on the gate insulating film over the gate electrode 11.
Subsequently, the plurality of data lines D1, D2, . . . , Dn are formed to cross the gate lines G1, G2, . . . , Gn. At the same time, the source and drain electrodes 13 and 14 are formed over the semiconductor layer 12. At this time, the data lines D1, D2, . . . , . . . , Dn have substantially the same width over the whole region of the panel.
As shown in FIG. 2C, a passivation film (not shown) is formed on the entire surface including the data lines D1, D2, . . . , Dn and the source and drain electrodes 13 and 14. A contact hole is then formed to expose the drain electrode 14. The pixel electrode 15 is formed to electrically connect with the drain electrode 14 through the contact hole.
At this time, since the respective pixel electrodes 15 have substantially the same area as one another over the whole region of the panel, they have the same aperture ratio as each other.
Thus, a TFT substrate is manufactured.
Although not shown, the TFT substrate and an opposing color filter substrate are prepared and attached to each other. A liquid crystal is then injected between the two substrates. Thus, the process for manufacturing the related art LCD panel is completed.
However, the related art LCD panel has several problems.
Since no electrode (pixel electrode) is formed before the first data line, after the last data line, or above the gate line, the electric field does not occur therein. Accordingly, in view of the whole region of the panel, the electric field intensity varies depending on the portion where the pixel electrode is formed and the portion where the pixel electrode is not formed, thereby causing difference in transmittivity therebetween.
According to the experiments, the transmittivity difference between the portion where the pixel electrode is formed and the portion where the pixel electrode is not formed is about 12%. Accordingly, luminance occurring before the first data line, after the last data line, or above the gate line is higher than that at the other portions. For this reason, picture quality is deteriorated.